An aircraft wing box typically includes a front spar, a rear spar, upper and lower covers (skins), spanwise stiffeners (stringers), and chordwise ribs. The wing box structure is typically manufactured in sections, which are joined together. Most commercial airliners have three wing box sections—a centre wing box structure in the fuselage and two lateral (left and right) wing box structures. However, the centre and/or lateral wing box structures may themselves comprise several wing box sections joined together by one or more spanwise joints.
In the typical three wing box section arrangement, the lateral wing box structures are joined to either side of the centre wing box structure by a “root joint”. FIGS. 1 and 2 illustrate schematic views of the central portion of one half of an aircraft 1, and show the location of the root joint 2 between the lateral wing box 3 and the centre wing box 4 embedded in the fuselage 5.
In a prior art arrangement shown in FIGS. 3 and 4, a root rib 111 forms the interface between the centre wing box 101 and the lateral wing box 106. Alternatively, the root rib can be considered to be part of either the centre wing box or the lateral wing box.
The covers and spars of the centre wing box and of the lateral wing box are typically joined to the root rib by several fittings. FIG. 3 illustrates a schematic section view of the central portion of the prior art root joint. The centre wing box 101 includes an upper cover 102 and a lower cover 103 extending between front and rear spars (not shown). The upper cover is supported by stringers 104 and the lower cover is supported by stringers 105. The lateral wing box 106 includes an upper cover 107 and a lower cover 108 extending between front and rear spars (not shown). The upper cover is supported by stringers 109 and the lower cover is supported by stringers 110. A root rib 111 forms the interface between the centre and lateral wing boxes 101, 106.
A plurality of corner fittings 112 are used to connect the wing boxes 101, 106 to opposite sides of the root rib 111. The base of each fitting 112 is fastened to one of the covers 102, 103, 107, 108 and to the foot of one of the stringers 104, 105, 109, 110. The end of each fitting 112 is fastened to the root rib 111. The side of each fitting 112 is fastened to the blade of one of the stringers 104, 105, 109, 110. The fasteners have been omitted from FIG. 3. A splice plate 113 is also fastened between the lower covers 103, 108.
FIG. 4 illustrates an array of the prior art fittings 112 used around the periphery of the lateral wing box 106. The lower row of fittings 112 are shown attached to their stringers 110. In addition to the fittings 112, spar fittings 114 are provided for connecting the front and rear spars (not shown) of the lateral wing box to the root rib.
As can be seen from FIGS. 3 and 4, the prior art root joint requires a large number of fittings and fasteners to form the joint, which causes a significant weight penalty. The large number of fasteners and alignment issues leads to a long root joint formation time on the aircraft final assembly line, which reduces productivity. The wing box interiors are typically used as fuel tanks, which can be difficult to seal due to the complex root joint. Moreover, the dihedral and sweep angles of the lateral wing box with respect to the root rib pose difficulties in terms of access for fastener tools used to fasten the wing box to the rib.
In more unconventional aircraft, which comprise several wing box structures joined together by spanwise joints (whether or not they appear at the actual wing root), the above-mentioned problems with the prior art spanwise joints are also evident.
There is therefore a need for an improved wing box spanwise joint, which addresses some or all of the above problems in the prior art.